Guayule is a desert shrub native to the southwestern United States and northern Mexico and which produces polymeric isoprene essentially identical to that made by Hevea rubber trees (e.g., Hevea brasiliensis) in Southeast Asia. As recently as 1910 it was the source of half of the natural rubber used in the U.S. Since 1946, however, its use as a source of rubber has been all but abandoned in favor of cheaper Hevea rubber and synthetic rubbers. Still, demand for natural rubber is expected to produce shortages of that material in the future and rubber prices are expected to rise significantly. Natural rubber having lower heat hysteresis is required for many kinds of tires and amounts to about 35% of U.S. rubber use.
As an alternative to synthetic rubber sources, attention is being directed to the production of hydrocarbons in plants such as guayule (Parthenium argentatum). Guayule normally yields one half ton to one ton of rubber per acre in cultivation when, after two years, the entire plant is harvested and processed. Guayule plants store latex in tiny inclusions in the bark, making harvest of the outer fibrous layers, or bagasse, of the plant, desirable.